An exhaust aftertreatment system associated with an engine may include a reductant supply system for delivery of a reductant into an exhaust stream of the engine. The reductant supply system may include a tank for storing the reductant, a pump, a reductant injector, and reductant delivery conduits. The reductant delivery conduits may fluidly connect various components of the reductant supply system for flowing the reductant therethrough. The reductant from the tank may be supplied to the reductant injector via the pump.
Some quantity of the reductant may be retained within components of the reductant supply system located downstream of the reductant tank with respect to a reductant flow direction after an engine shutdown. The reductant is susceptible to freezing in cold environments. For machines operating in relatively cold environments, the reductant contained within the components of the reductant supply system may freeze, which may in turn affect performance of the aftertreatment system. Therefore, aftertreatment systems may benefit from an ability to purge the components of the reductant supply.
U.S. Patent Publication Number 2013/0000743 (hereinafter the '743 publication) describes a selective catalytic reduction system that includes a fluid distribution system for supplying an exhaust gas reducing agent. The system includes a liquid storage tank and a fluid distribution module with a fluid pump that draws liquid reducing agent from the tank volume and provides the liquid at a module outlet port, while simultaneously discharging excess liquid from a circulation line outlet within the tank volume. The circulation line outlet of the '743 publication can be located at a bottom portion of the tank volume near other distribution module components to promote liquid circulation around the module components during a fluid distribution period, to promote thawing of frozen reducing agent at and around the module components, and to ensure a continuous supply of liquid to the fluid pump.
Fluid may be purged from components in the '743 publication by reversing an operating direction of the reductant pump. However, such a purge strategy does not apply to reductant supply systems that do not include a pump in contact with the reductant. Alternatively, fluid may be purged from components in the '743 publication by applying pressurized air to the system that drives a mixture of air and reductant through the pump and into the tank. However, the air purge strategy of the '743 publication calls for a separate pressurized air system in addition to the liquid pump, which may be expensive and complex. Hence, there is a need for an improved reductant supply and purging means in exhaust aftertreatment systems.